The invention relates to dialyzer coils useful in artificial kidney machines, and more particularly to an improved support for the membrane material to insure the desired turbulent flow characteristics for the dialysate and the provision of a preferred flattened configuration for the blood flow channel between adjacent layers of membrane material.
Prior to the present invention, dialyzer coils for artificial kidney machines have evolved through several stages of improvement, each to the benefit of patients suffering from acute or chronic renal failure. Early coils using an over-and-under woven mesh material as a support for the tubular membranes are disclosed in Metz U.S. Pat. No. 2,880,501 (1959) and Broman U.S. Pat. No. 2,969,150 (1961). Gobel U.S. Pat. No. 3,077,268 (1963) discloses the use of a hobnail configuration on both sides of impervious support material, rather than woven plastic mesh, and this support can be located either inside or outside the flattened tube of membrane material.
A significant improvement in dialyzer coil design was brought about by the use of a particular non-woven plastic netting disclosed by Kolobow in "A New Dynamic Disposable Artificial Kidney," Transactions, American Society for Artificial Internal Organs, Volume X, pages 116-120 (1964), and Proceedings, Conference on Hemodialysis, (Nov. 9-10, 1964) National Institute of Health, Bethesda, Maryland, pages 87-94. The same non-woven plastic netting is disclosed as being useful in a multiple-start-spiral design of dialyzer coil in Hoeltzenbein U.S. Pat. No. Re 27,510 (1972), a preferred orientation for the non-woven strands of the Kolobow netting is disclosed in Miller U.S. Pat. No. 3,508,662 (1970), and a particular cross-sectional shape for such strands is disclosed in Martinez U.S. Pat. No. 3,709,367 (1973).
The use of non-woven netting was responsible for many advantages in the performance and operation of dialyzer coils, not the least of which was a substantial reduction in the cost per unit because it facilitated commercial manufacturing procedures, including the elimination of edge spacers. Certain problems, however, were not solved by the use of non-woven netting, and others were created by its use. Problems in the former category include unwashed areas where the strands of netting contact the membrane, preventing 100% utilization of the available membrane area. In the latter category, the use of non-woven netting may cause manufacturing difficulties because the delicate membrane material is subject to puncture and tearing by the exposed ends of the plastic strands along each edge of the support material. In addition, the use of non-woven netting defines diagonally crossing chambers or pouches in the blood flow passage as the membrane distends under pressure, which militates against the ideal of a uniformly thin blood passage in which as great a percentage as possible of the blood is in contact with a membrane wall during passage through the dialyzer coil. Such distention under pressure requires the use of netting sufficiently thick to prevent blockage of the dialysate flow by the distented membrane, and the thicker the netting the greater the maximum blood volume and change therein as the flow and/or pressure is varied.
In 1971, Frost of the Department of Mechanical Engineering at the University of Newcastle Upon Tyne made reference to the use of a flat mat of porous nickel foam by Babb et al, "Clinical Experience With the Babb-Grimsrud High Efficiency Dialyzer," Proceed. Europ. Dialysis and Transplant Association, 4, p. 114-120, published by Excerpta Medica (1967). But the nickel material proved unsatisfactory, and thickened edge portions were deemed necessary for spacing purposes because all surfaces were relatively smooth without embossments.
Thus, the problem heretofore unsolved by the prior art is a dialyzer coil which is inexpensive and virtually foolproof in manufacture, which mandates a uniformly thin passage for blood between adjacent membrane walls by restricting undesireable distention thereof, and which directs dialysate to wash against the opposite sides of the membrane walls with the required turbulent flow and with a minimum of unexposed areas.